Pressure synthesis loop, effect

With increasing pressure, ammonia formation increases (Fig. 78). This results not only from the more favorable equilibrium situation for the reaction, but also from the effect on the reaction rate itself. In industrial practice, there are plants that operate at about 8 MPa (80 bar), but there are also those that operate at more than 40 MPa (400 bar). Today, plants are built mainly for synthesis pressures of 150-250 bar. Typical operating parameters for modern synthesis loops with different pressures are listed in Table 34. 

The effect of synthesis loop pressure on the relative investment of the compressor factory and running power of the compressors for the plant is shown in Fig. 9.14. It can be seen from Fig. 9.14 that in the above range of synthesis pressure, the power change is small (about 6%). The influence of synthesis loop pressure on investment is obvious. Pressure rising makes the investment of compress section increase by 20% or more. 

The synthesis loop uses a horizontal converter in which the catalyst beds are arranged as horizontal slabs (Fig. 7.8). This configuration results in a very small catalyst pressure drop, and this enables small catalyst particles to be used with a subsequent increase in the effectiveness factor of the catalyst. In this way the process effect is very similar to a radial flow converter. 

The adverse effect caused by a high concentration of water has also been demonstrated on an industrial scale. In a partial oxidation plant with a liquid nitrogen wash, about 100 ppm of oxygen leaked into the synthesis loop, giving an [0] content in the inlet gas of about 20-30 ppm. This resulted in an immediate activity decline. The pressure was increased as well as the temperature. However, the production declined somewhat. After some months of operation, the oxygen contaminant was removed and the catalyst regained its former activity. 

The recycled gas is routed to the recycle compressor after the purge gas is withdrawn through a pressure controller. Here it is brought up to the makeup gas pressure and mixed with this gas. The makeup gas can also be mixed with the recycle gas on the suction side of the recycle gas compressor. The feed point is stipulated appropriate to the pressure increments of the synthesis gas compressor and possible heat recovery in the condensation area of the loop. Generally, common compression of makeup and recycle gas in the recycle compress effects a... 

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